This is a continued effort of collaborative multi-phase project to investigate the immune response in both human and experimental animals after the infection with human hepatitis C virus. In the initial phase, the commercial testing kits will be used to detect antibodies to HCV proteins in the known non-A, non-B hepatitis patient sera. This will provide information on the serological data of hepatitis C virus infection and its relationship to other clinical determinations. The second phase of the study will be concentrated on the identification of immune dominant epitopes and neutralizing epitopes. The scope of this phase of study will be extensive and time-consuming. The third phase of the project will encompass using the knowledge of immune response to develop preventive strategy and understanding the pathogenicity of this viral infection. Special attention will be paid to the possible relationship between immune response and the high chronicity in patients.